The third-seeded Radwanska faced little resistance against Kerber, who advanced to the semis after top-ranked Victoria Azarenka withdrew Thursday after a bout of dizziness in her third-round match a day earlier.

Radwanska dominated from the outset, breaking Kerber six times, including in the final game when the German played some of her best tennis, staving off three match points.

Despite the relative ease with which she won, Radwanska said it was tougher than it appeared.

"We played before and it's always tough against her,'' she said. "I had to run a lot. She's a great player and I really had to stay focused.''

Petrova set the pace early when she broke Stosur in the first game, and she had nine aces in the match.

Any chance for a comeback by Stosur was dashed when Petrova broke the ninth-seeded Australian in the seventh game of the second set to go up 5-2.

"When I arrived here, I wasn't sure if I was going to be able to play at all because I didn't feel well,'' Petrova said. "But I got stronger and stronger with every match and am happy to be in the final.''